Annihilation boasts one of the most audacious climaxes in recent cinema history, and its music is just as haunting. The film finds director Alex Garland – whose directorial debut was 2015’s Ex Machina ­– again tapping the duo of Geoff Barrow and composer Ben Salisbury for the soundtrack, one that matches the unsettling, psychedelically altered terrain of the mysterious swath of swampland called “the Shimmer.”

Barrow is best known for his brooding work in the critically acclaimed trio Portishead and Salisbury has a scoring résumé that ranges from numerous David Attenborough natural history TV series to Beyoncé: Life Is But a Dream. Both hail from Bristol and began working together on the Garland-produced 2012 feature Dredd. Their score ultimately wasn’t used, but they’ve since worked on Ex Machina, Ben Wheatley’s Free Fire and episodes of Black Mirror and . With Annihilation, the duo crafted a mind-altering soundworld with acoustic guitar, orchestra, a touch of electronics and a four-note motif. Rolling Stone reached out to the duo in their respective Bristol homes.

How long have you known each other?Salisbury: Funny enough, it’s through football, which we are about to play. We started playing football 15 years ago. Neither of us knew what each other did. I didn’t know Geoff was Geoff from Portishead.

Barrow: And I didn’t know Ben did TV music. We usually analyzed how bad we were at football in the bar afterwards and never really got onto music. It was the Spanish Inquisition on a weekly basis. It’s a way for everyone to leave their lives, families, work at home. A lot of people play sports to network, but for us it was the opposite.

Salisbury: After about five or six years of playing weekly football, I realized who Geoff was and had a question about clearing samples. And then we were talking about music. I did some string arrangements for bands on Geoff’s label, Invada, and he was doing music for Exit Through the Gift Shop, and we had a vague idea to work together on that, but it didn’t materialize. I was stuck doing music for natural history films and you only get to write one type of music for them. I was being suffocated. And Geoff was looking for a way to write for feature films. We both saw teaming up as a way to break out of our respective slots.

Barrow: It’s about the actual art of being able to write music for films. That was the thing that Ben had studied and, as a combination, we got on as people, so the idea of collaborating was natural. In the beginning, Ben was good with scoring and I didn’t know where a cue would sit. It’s fairly different now, you’ve learned things that I do and I learned what you do. Now we can go straight into a job feeling confident about ourselves because we had each corner covered.

Portishead’s “cinematic” qualities are always quite evident in your albums. Were film scores and soundtracks always an ultimate goal of yours?Barrow: No, not really. We were just very much into soundtracks. The experiments of film composers, whether they were orchestral or whatever, you can look at Lalo Schifrin using James Brown beats with [esoteric percussion instrument] waterphone and choir voices and synths. You just go, “Wow!” It’s a massive combination. Adrian Utley and I had that friendship through films. He was into The Ipcress File [by John Barry] and I was into John Carpenter. And that’s how Ben and I got along.

Salisbury: Film scores – especially where Geoff and I grew up in Bristol – were our gateway into interesting music. We all heard Beatles records and whatever classical music our parents played, but I didn’t hear interesting classical music until I saw Planet of the Apes.

Or you see 2001: A Space Odyssey and get to hear the György Ligeti choirs.Salisbury: Yeah, it’s a gateway drug into the world of interesting music. You hear like Tangerine Dream in Risky Business and you go “I love that” and then you read somewhere where Steve Reich gets mentioned and suddenly you’re into a different world of music. That made me want to write film music. Bristol is the home of natural history and my dad worked in natural history, but film dramas drove both of us.

Drokk was your first collaborative film score, but it was rejected for Dredd?Salisbury: Rejected is a strong word. It was a “no.” We started work on Alex Garland’s film for Dredd. Geoff came up with this very strong – but particular – idea for the film. Alex loved it, but the finances for the film eventually thought the whole project was becoming too “art house” for them and the music was part of that. We knew this was going on and there was an opportunity to water down what we were doing.

Barrow: For me, I grew up with 2000 AD so it was a massive influence on me. When the Dredd film came around, I had to do it to my beliefs or you don’t do it at all. The last thing I wanted to do is have 200,000 2000 AD fans going, “You wrote shit music for that film.”

Salisbury: We can take notes and take direction, but for that particular project, we had to abandon it rather than add electric guitars to the music. That’s why we didn’t do the soundtrack but carried on working with Alex.

How was the process different from Ex Machina and Annihilation?Barrow: Working properly with Alex is one difference. We were on from the very first cut. It’s intense working on an Alex Garland film. You end up writing the score five times over some times, because things change.

Salisbury: To have your say in terms of narrative elements of Annihilation is incredible. It’s a five-part team: editor Barney Pilling, me, Geoff, Alex and music editor Yann McCullough.

Barrow: It’s an intense way of working. We were on it for a year and most of the time you feel like you’re going backwards. It’s really strange. It feels like spinning plates. You nail a cue, but then Alex would move that onto another part of the film. You want to kick his head in! [Both laugh.]

Salisbury: You build this beautiful building and then you knock out a pillar.

I also never thought I’d see the day when I could hear Geoff’s music alongside Crosby, Stills & Nash.Salisbury: That was Alex, but the film had two set pieces of music. There’s a minute of Moderat’s “The Mark” and this Crosby, Stills & Nash song, “Helplessly Hoping.” They were poles apart, but it gave us some foundation. CS&N gave us this acoustic guitar thread and Moderat gave the end of the film this electronic feel at the end. As soon as we heard both of them, we went, “They’re great.”

The use of steel string finger-picking sounds so distinct than what you usually hear in science fiction films of this ilk.Salisbury: Films that Annihilation vaguely references – like Southern Comfort – those searching-in-jungles-and-backwoods-of-America-type films, it just felt right to put acoustic guitar there. Not just right, but also a little bit odd in a sci-fi film.

Barrow: Most sci-fi films start now with huge orchestral armies of synth and sound design. And this was a bit of a human story so it was really important to just give it a sense of reality rather than going into Marvel synthworlds. It had to get somewhere.

Salisbury: We knew the film had to go from suburbia to psychedelic insanity. You have to get there, but you can’t get there by front-loading it all in the score.

Barrow: Another film I recently caught, once they did the big thing 10 minutes in, it was like, “Man, where are you going to go from there?” And to be honest, they didn’t go anywhere. By the end of it, the synths were screaming so hard like ‘Gaaarrrrrgh‘ like they were trying to wring something else out of it, because they had already done it in the first 10 minutes of the film.

One of the film’s themes is the corruption of form, wherein every character’s DNA becomes affected by “the Shimmer.” And as the movie goes on, the soundtrack seems to musically mimic that same sense of decay.Barrow: We did something similar for Ex Machina, taking the theme and running it through a simple distortion bit-cruncher thing. It takes you on a journey.

Geoff Barrow and Ben SalisburyCuts

Salisbury: What you picked up on was very important. And managing that and judging the temperature of that, and not getting too weird too soon and saving a massive thing for the climax was important. When we first … saw the alien sequence in the lighthouse, we were blown away by it. And we just had to keep hold of that feeling we had when we first saw it. We knew it would be a 12-15-minute long music sequence and we found good temp music, some chorale music, which worked well.

But we knew we had to write for that in the end and it was a massive challenge. The piece itself, “The Alien,” has four sections: Geoff and I took charge of the orchestral part, Geoff handled the electronic part, and the voices one I took charge of. But the stitching together of it was Alex and Barney and it was an interesting collaboration.

Barrow: Actually, we wanted to stay away from synths in the whole film. We really were not interested at all in using them. For the early part of the film, all the weird noises are all waterphone. It’s this hippie kind of Californian weird instrument that you pour water into, but they were used a lot in the Seventies as sound effects.

Salisbury: They’re in Lalo Schifrin’s score for Dirty Harry, but it’s used as a sound effect. But we tried to get a waterphone choir out of it. I would sit in the control room and sing the note and Geoff would try to bow that tone out of it. It’s like a steel octopus. Because it’s not tunable, it would never produce perfect results, it always wobbled and was weird. And it was perfect for the Shimmer.

Barrow: We got through this whole portion of the film without synths. So for the lighthouse scene, now we just need to hit people in the chops a little bit. As we hadn’t used electronics, it seemed like the right time for it.

Salisbury: There’s this four-note motif that people are going on about, this alien sound, and I don’t know if people noticed, but the seeds for that had been sown throughout the film in a harmonic way. It’s in the guitar pieces. It’s all simple stuff, those four notes come in as harmonic bed with the waterphone and strings.

Barrow: We’re massively into themes, the idea of properly using themes. That really does it for us.

Salisbury: That four-note theme was much bigger in the original version of the film. But Alex wanted to save it for the climax. Now when you watch the film, you get the impact of that moment. The Shimmer, there was this talk about getting this balance between beauty and fear. They’re terrified and entranced by it. There was never going to be a “guns blazing” part to the film.

What was it like finally seeing how the lighthouse sequence played out on-screen?Salisbury: It was one of the first things they got together in the first cut we saw, just without the CGI. You just had the dancer and Natalie doing their strange dance. And even then, it just blew us away. I remember coming out of that first screening and thinking, even if nothing else works and they manage to keep hold of the feeling we got from that final dance scene and meeting the alien, it’s going to be brilliant.

Barrow: It was always that thing, wasn’t it? How are they going to get this past Paramount? [Both laugh.] How are they going to get it intact into the cinema?

Salisbury: For some people, the whole thing winds them up. The music is shouting at you and everything is full on. So fair enough. Alex’s decision to go for it, there’s no point in smudging around the edges. The audience we saw it with, you could feel their jaws dropping.

Barrow: I went to the L.A. premiere and you needed a stiff drink after it. The afterparty was a real damp squid. Everyone was just staring at each other in disbelief.